System and method for providing active RF shielding

ABSTRACT

A system and method for removing radio frequency emissions from an electronic device. The system comprises collectors for collection of the radio frequency signals, combiners for combining the signals to produce a combined signal, fiber optic transmitter for up-converting the combined radio frequency signals to an optical wave length signal, optical fiber for directing the optical signal, and a heat sink for terminating the optical signal.

BACKGROUND OF THE INVENTION

This disclosure relates generally to methods and systems for radiofrequency (“RF”) shielding of electronic devices. Electronic devices areconsidered ubiquitous in today's society. Electronic devices are foundeverywhere and are used by everyone. Many electronic devices emit RF andmany times can receive unintentionally spurious RF transmissions. Forexample, a common experience is the interference created when using amicrowave and a cordless phone at the same time. The RF emissions fromthe microwave may interfere with the operation of the cordless phone andrender the cordless phone inoperable until the microwave is turned off.Another common experience is the interference created when using amicrowave and a WiFi router at the same time. In this example, the RFemissions from the microwave may interfere with the operation of theWiFi router and render the WiFi inoperable until the microwave is turnedoff or the WiFi router is switched to a different frequency. These arecommon examples that demonstrate that microwave ovens have RF emissionsthat may interfere with other devices that rely on RF forcommunications. More information about RF emissions from variouselectronic devices can be found in, “Study of RF Emissions of VariousElectronic Devices Used by the Public” by Letertre et al., which ishereby incorporated by reference.

When referring to RF emissions that interfere with other electronicdevices, sometimes it is referred to as radio frequency interference(“RFI”) or electromagnetic interference (“EMI”). Some may describe theemission of RF from an electronic device such as a microwave as RFleakage. However, in the present invention, the reference to radiofrequency (“RF”) will refer to any of RF, RFI, RF leakage, EMI, RFenergy, and spurious RF transmissions.

Hackers and/or enemies-of-the-state (“Hackers”) can utilize RF emissionsto hack into systems, attack systems, spy/monitor on systems, or disruptsystems. Hackers may target electronic devices such as computers,routers, appliances, mobile phones, cordless phones, switches, computermonitors, game consoles, DVD players, control electronics and otherelectronic devices that are likely to emit RF signals that could bedetected by sensors located onboard an enemy platform including but notlimited to ground-based, airborne and/or space-borne platforms. The RFemissions from such devices may comprise keyboard strokes, computermonitor images, drawings, private data, business data, financial data,political data, defense data, internet URLs, URL history, IP addresses,cookies, real time data, stored data, meta data, device usage data,electronic records, electronic files, video, audio, control signals, orany type of data, information or signal that an electronic device maycontain or emit.

A sophisticated enemy may use a sensor to detect RF emissions to insertan external RF hacking signal that may be comprised of one or more ofviruses, noise, or other enemy directed RF signals. In other situationsa sophisticated enemy may use the detected RF emission locations todirect a high energy laser (“HEL”) or an IREB (Intense RelativisticElectron Beam) system at those locations to physically destroy theelectronic device. In other situations a sophisticated enemy may use asensor to detect and monitor the RF emissions from certain electronicdevices for intelligence purposes. Examples of where an enemy or hackermay be interested in RF emissions might be at a utility plant (i.e.electric, gas, water, solar, oil etc. . . . ) or at a corporatecompetitor. Hackers may detect RF emissions and use techniques mentionedabove to disrupt or destroy elements of the utility plant.

In order to control RF/EMI, an industry has developed around shieldingmaterials. Shields are measured by its “shielding effectiveness” (SE).An electro-magnetic (EM) shield is essentially any barrier placedbetween an EM emitter and a receptor, and it is designed to reduce thefield strength of the emitter. The losses in EM emitter field strengthare a function of the barrier's electrical and physical characteristics,such as its permeability, conductivity, and thickness; the frequency ofthe EMI; and the distance from the EMI source to the barrier/shield. Thetotal SE of the shield is the sum of the reflection, absorption, andre-reflection losses. For more information see “Eyeing EMI/EMC In RFDesigns,” by Jack Browne, Microwaves & RF (www.mwrf.com), June 2011,which is hereby incorporated by reference.

One method of shielding electronic devices comprises placing theelectronic device in a box made of metal such as aluminum, steel orcopper. In this method the electronic device continues to emit RF,however most of the RF emission is contained inside the box and notallowed to escape the box. Other methods include placing the electronicdevice in an enclosure made of metal screen such as a Faraday cage.Other methods include shielding entire rooms with metal and placingseveral electronic devices in such rooms. Shielding material may be madeof metal, metal screen, woven-in metallic fabric, foam, or can be ametalized paint. In a building, windows can have special metalliclouvers or embedded metal screens to minimize RF leakage. All of thesemethods are referred to as passive shielding solutions. The problem withpassive shielding solutions is that RF still leaks. In other words, theRF signals still escape from the enclosure. Generally these passiveshielding solutions dampen but do not eliminate RF emissions.

Shielding has also been used on individual components of a circuitboard. Again this approach is considered passive shielding. Evenencasing a component in metal does not eliminate the RF emissioncompletely.

BRIEF SUMMARY OF THE INVENTION

In various embodiments the invention provides for the active RFshielding of electronic devices. In one aspect, the invention provides asystem and method for detecting, collecting, up-converting, directing,and terminating RF emissions from an electronic device. In one aspect ofthe invention, RF emissions are detected and located on an electronicdevice. In another aspect of the invention, both the radiative andconductive aspects of the RF emission are collected. In another aspectof the invention, RF is up-converted to laser wavelength-band anddirected onto optical fiber cable. In another aspect of the inventionthe optical fiber is terminated by a slightly tilted mirror which facesthe incoming laser plus the optical equivalent of its associated RFsignal. In one embodiment of the invention, the system is an analogimplementation of the invention. In another embodiment of the invention,the system is a digital implementation of the invention. In anotheraspect of the invention, voltage and/or current spikes or transients dueto shock, vibration, heat, cold are captured and dampened, reduced oreliminated. In another aspect of the invention, filters are utilized tocapture various bandwidths of RF emissions.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrated in the accompanying drawing(s) are embodiments of thepresent invention. In such drawings:

FIG. 1 is a diagram showing one aspect of the invention, two computernetworks configured to communicate via a synchronous satellite;

FIG. 2 is a diagram showing one aspect of the invention, a networksubject to an enemy/hacker on a different floor of a building;

FIG. 3 is a diagram showing one aspect of the invention, directing a RFhacking/monitoring signal from one building to the other;

FIG. 4 is a diagram showing one aspect of the invention, a logicaldiagram of the RF emissions from an electronic device from capture totermination of the RF emission;

FIG. 5 is a flow diagram of a method showing one aspect of the inventionfor active RF shielding (“ARFS”);

FIG. 6 is a diagram showing one aspect of the invention, a circuit boardwith three locations having EFI leakage that are in need of active RFshielding;

FIG. 7 is a diagram showing one aspect of the invention, a diagram ofthe RF emissions from an electronic device from capture to terminationusing digital components;

FIG. 8 is a flow diagram of a method showing one embodiment of theinvention for a digital implementation of RF shielding (“ARFS”).

The above described drawing figures illustrate the described apparatusand its method of use in several preferred embodiments, which arefurther defined in detail in the following description. Those havingordinary skill in the art may be able to make alterations andmodifications to what is described herein without departing from itsspirit and scope. Therefore, it must be understood that what isillustrated is set forth only for the purposes of example and that itshould not be taken as a limitation in the scope of the presentapparatus and method of use.

DETAILED DESCRIPTION OF THE INVENTION

Active RF shielding (“ARFS”) is achieved by up-converting RF emissionsfrom an electronic device to a laser wavelength-band which will then befed into a fiber optic cable and then terminated. Fiber optic cables areused because optical fibers are immune to electromagnetic interferenceand do not leak electromagnetic radiation or RF. This insures that theup-converted laser signal will be kept within the optical cable and thusnot radiate outside of the fiber optical cable. The fiber optic cable isconnected to a heat sink where the signals are terminated. Terminatingthe signals using a heat sink ensures the minimizing of RF emissions.Further, since optical cables do not leak RF nor laser signals, they aredifficult to tap into without being detected. To further reduce theintensity of the output of the upconverter subsystem, as theup-converted laser signal enters and navigates through the fiber-opticcables, there may be placed within the cable, a number of patches whosefunction is to absorb, scatter and reflect-backwards the laser signal,as it moves through the cable. The patches are approximately 1 cubic cmin size and are material such as small sized rocks and a bit of sand.The patches may also contain small bags of sand. The bag material ismade of cheese cloth or other loosely woven fabric.

FIG. 1 depicts a diagram of a computer communications network 101, twocomputer networks 121 and 123 configured to communicate via ageosynchronous satellite 103. Computer network 121 comprises server 115,router 117, and PC 119. Computer network 123 comprises server 129,router 127, and PC 125. Each computer network is connected to a groundstation 113 and 131 respectively. Although not shown, each computernetwork 121 and 123 may comprise multiple PCs, multiple routers, andmultiple servers.

Although not shown in FIG. 1, the geosynchronous satellite 103 can beremoved from the diagram and replaced with an Internet cloud. In otherwords, the two computer networks 121 and 123 can communicate with eachother via the Internet and not necessarily with just the geosynchronoussatellite 103. In this case ground stations 113 and 131 may besubstituted with gateways or other devices to enable Internetcommunication.

FIG. 1 depicts a situation where network 101 is vulnerable to anenemy/hacker intercepting RF emissions from any of the network devicesdepicted. Network 121 is also vulnerable to an external RF hackingsignal that could be received at ground stations 113 or 131. The dottedlines around servers 115 and 129, routers 117 and 127, PCs 119 and 125represent the RF emissions from these devices. These RF emissions may bereceived by sensors on-board platforms such as UAV 111, surveillanceaircraft 109, airship 107 and low earth orbiting (“LEO”) satellite 105.Additionally, communication links 133 and 135 from each of the groundstations 131 and 113 emit RF and can also be intercepted by UAV 111,surveillance aircraft 109, airship 107 and LEO satellite 105 or a groundbased person or vehicle (not shown). The RF emissions depicted innetwork 101 presents a very lucrative situation for a hacker because itis vulnerable to enemies and hackers. Network 101 is both a treasuretrove of information to be gained and an opportunity for many differentpathways to inject hacking signals into the network.

FIG. 2 depicts a situation where a vulnerable network is located atposition 205 on the 20^(th) floor of a building 207 and an enemy/hackerlocated at position 203 on the 23^(rd) floor of the building 207. Thevulnerable network located at position 205 on the 20^(th) floorcomprises computers, routers, and servers leaking RFI similar tocomputer networks 121 or 123 leaking RFI in FIG. 1. From the 23^(rd)floor at position 203, an enemy/hacker is able to monitor or attack thevulnerable network located at position 205 on the 20^(th) floor. Thevulnerable network located at position 205 could benefit from thepresent invention.

FIG. 3 depicts a situation where an enemy/hacker located in building 307is monitoring leaking RFI signals or inserting a hacking signal intoleaking RFI signals emitted from a vulnerable network located atposition 311 in building 309. The vulnerable network located at position311 comprises computers, routers, and servers leaking RFI similar tocomputer networks 121 or 123 leaking RFI in FIG. 1. An enemy/hacker setsup antenna 305 on building 307 for the purpose of monitoring and/orinserting a hacking signal into network located at position 311. Theenemy/hacker may use the RFI to determine position information such asthe coordinates, GPS coordinates, world coordinates, or the location ofthe RFI source. The enemy/hacker using such position information maydestroy the RFI position using an airborne missile or other means oftargeting and destroying. The vulnerable computer network located atposition 311 could benefit from the present invention.

FIG. 4 depicts the active RF shielding (“ARFS”) solution 401 and itscomponents which comprise collectors 403, 405, 407, an RF combiner 409,a fiber optic transmitter 411, a fiber optic cable 413, and optionally aheat sink 415.

403, 405, and 407 depict three of N RFI collectors (where N is the totalnumber of collectors). The RFI collectors 403, 405, 407 may collecteither RF that is conducted via wires or RF that is emittedelectromagnetically from an electronics device (not shown). Thecollector will be different depending on the type of RF collected eitherconduction through physical wires or electromagnetic radiation.

In one aspect of the present invention, conductive collectors are usedto collect conductive RFI. Conductive collectors may be grounded coppershielded wires, coaxial cables or other type of conductive elementcapable of conducting RF. The conductive collectors are each connectedto an appropriate conduction point on the circuit board. Such aconduction point may be, for example, a solder joint that isconducting/leaking RFI. Other conduction points may include via's,leads, or any type of surface that may exist on an electronic device.Conduction collectors may be tuned to the bandwidth, frequency orfrequencies of the conducted RF using a tuner for each conductioncollector. Such tuner may comprise a tank circuit or a parallelcombination of a capacitor (C) and an inductor (L) type circuit. Thetuning elements of a conduction collector are not shown in FIG. 4.Additionally, a filter may be connected between a collector 403, 405, or407 and the combiner 409. The filter may be connected before or afterthe tuner (not shown in FIG. 4). In the event that a filter is usedprior to the tuner then we may refer to this filter as a pre-filter. Thefilter may be used to isolate certain bandwidths or frequencies ofinterest. For example, a high pass filter may be used to collect onlyfrequencies above a certain threshold frequency. In another aspect, alow pass filter may be used to collect only frequencies below a certainthreshold frequency. Other filters may be used such as notch filters orband-pass filters. In another aspect, any combination of filters may beused to isolate certain bandwidths or frequencies of concern. In someaspects of the present invention, the filter may in fact be the same asthe tuner.

In another aspect of the present invention, radiative collectors areused to collect RF electromagnetic radiation emanating from specificlocations or areas of a circuit board. Radiative collectors may besmall/micro/nano antennas. The antennas may be designed to receive asingle frequency or frequencies emanating from an RF radiation locationor from multiple locations. In one aspect of the invention, the antennasmay be micro-electro-mechanical (“MEMS”) devices. These antennas may besmall enough to fit on a microchip. The antennas may be an array of MEMSantennas or could be just a single antenna. In other aspects of theinvention the antennas may be horn antennas or parabolic antennasconfigured to receive the RF electromagnetic radiation. However, in eachcase, the antenna will be designed to receive the bandwidth, range offrequencies or single frequency emanating from the one or more targetedRF sources on the circuit board. The tuning elements of a radiativecollector are not shown in FIG. 4. Radiative collectors may be tuned tothe bandwidth, frequency or frequencies of the radiated RF using a tunerfor each radiative collector. Such tuner may comprise a tank circuit ora parallel combination of a capacitor (C) and an inductor (L) typecircuit. The tuning elements of a radiative collector are not shown inFIG. 4. Additionally, a filter may be connected between a collector 403,405, or 407 and the combiner 409. The filter may be used to isolatecertain bandwidths or frequencies of interest. For example, a high passfilter may be used to collect only frequencies above a certain thresholdfrequency. In another aspect, a low pass filter may be used to collectonly frequencies below a certain threshold frequency. Other filters maybe used such as notch filters or band-pass filters. In another aspect,any combination of filter may be used to isolate certain bandwidths orfrequencies of concern. In some aspects of the present invention, thefilter may in fact be the same as the tuner.

The outputs of the collectors 403, 405, and 407 may optionally be routedto an enclosure connector that may be mounted to the outside of theenclosure of the electronic device. The enclosure connector is not shownin FIG. 4. However, the enclosure connector may be between thecollectors and the combiner 409. In such an implementation, the presentinvention may be a modular device containing an external connector thatconnects to the enclosure connector on the outside of an enclosure andprovides elements 409, 411, 413, and optionally 415. In this embodiment,a manufacturer could collect RF leakage and route the collected signalsto an enclosure connector. Then the remainder of the invention could beconnected as an external connector as a separate but optional piece ofhardware to that device. Once each of the locations of the RF energy hasa collector connected to it using the types of collectors describedabove, the RF is then carried to an RF combiner 409.

In one aspect of the present invention, the RF combiner 409 is any oneof the commonly available RF combiners sold by Mini-Circuits, Inc.(www.minicircuits.com) or L-com, Inc. (www.1-com.com). The RF combiner409 adds-up or sums the various collected RF signals. In other aspectsof the present invention, the RF combiner comprises analog operationamplifiers configured to sum the input RF signals. The configuration ofthese operational amplifiers to sum the RF signals is known to those ofskill in the art and discussed further in “Operational Amplifiers:Integrated and Hybrid Circuits”. Examples of such operational amplifiersare provided in “Op Amp Circuit Collection” by National Semiconductor,Application Note 31, September 2002, which is hereby incorporated byreference. The output of the RF combiner 409 connects to the input of afiber optic transmitter 411.

The fiber optic transmitter 411 up-converts the combined RF signals toan optical signal (laser wavelength-band). The fiber optic transmitteris a common device as is known in the art. Fiber optic transmittersconvert an incoming pulse (voltage) into a precise current pulse todrive any one of LED, Fabry-Perot Laser, DFB Laser, or vertical cavitysurface-emitting lasers (VCSEL). Lasers generally are biased with a lowDC current and modulated above that bias current to maximize speed. Inone aspect of the present invention, the fiber optic transmitter may beselected from the various fiber optic transmitters supplied by Miteq,Inc. (www.miteq.com). Selection of the fiber optic transmitter maydepend on certain parameter selections known to those of skill in theart and discussed further in “Fiber Optic Essentials”, by CasimerDecusatis et al., which is hereby incorporated by reference. Otherexamples of fiber optic transmitters may be found at ViaLiteCommunications, Inc. (www.vialite.com). ViaLite Communications, Inc.,sells optical transmitters that are capable of converting RF signals tooptical signals using laser diodes. One advantage of up-converting thecombined RF signal (that is output from the RF combiner 409) to anoptical band, is that it continuously eliminates the combined RF signaland therefore removes existing RF leakage. Fiber optic signals once onthe core of the fiber do not have RF emissions. The fiber optictransmitter outputs the up-converted signal into a fiber optic cable413.

In one embodiment, the fiber optic cable is terminated using a heat sink415. The heat sink 415 is not a required element in the presentinvention. However, it is necessary that the optical signal getterminated or dampened. The heat sink 415 absorbs or terminates thesignals in the fiber optic cable, thus removing much of the up-convertedRF. The heat sink 415 may be composed of various ways to attenuate theup-converted/optical signal. In some aspects, the heat sink 415, mayabsorb or scatter the signal. In another aspect of the presentinvention, the heat sink 415 may be of a design disclosed in U.S. Pat.No. 6,643,447 by Guy et al which is hereby incorporated by reference.Guy, et al describes a heat sink in which optical energy transmittedfrom the output end of a fiber optic cable is reflected repeatedlybetween two mirror image involute-shaped cavities to prevent opticalenergy from being reflected back in to the output end of the opticalfiber thus achieving an attenuation. Since the optical fiber is notcarrying a communications signal, the reflection of optical light backupstream to the fiber optic transmitter in some embodiments is not afactor. In other aspects of the present invention, the heat sink 415 isan optical signal absorbent material such as sand. The end of theoptical fiber 413 can be inserted into sand and the sand will absorb theoptical signal and provide the necessary attenuation of the opticalsignal. In other aspects of the present invention, a heat sink may notbe used. For example, the optical fiber may be wound up in a coil. Inthis case, the fiber optic cable must be long enough for sufficientattenuation to occur, for example, 10 feet. However, shorter lengths ofoptical fiber may be sufficient depending on the situation.

FIG. 5 depicts a flow diagram of a process for providing ARFS. Theprocess may be performed by some or all of the system of FIG. 4. Processelements in FIG. 5 may be executed individually or in combination withany of the elements of FIG. 5.

In one embodiment, the RF energy radiated and/or conducted by anelectronics device is detected as shown in block 501. The RF may bedetected manually with a spectrum analyzer using a near field probe. TheRF may also be detected automatically using automated methods. TheSpectrum Analyzer is a measurement instrument which performs a FourierTransform and displays the individual spectral components that make upthe time domain signal. The phase may or may not be preserved, dependingon the design of the Spectral Analyzer. A detailed discussion of theSpectrum Analyzer is given in “Spectral Analyzer Basics”, ApplicationNote 150, by Agilent Technologies, Inc., which is hereby incorporated byreference.

The location and frequency of the RF is recorded. The spectrum analyzerand near field probe combination will allow for the pinpointing of RFsources on or emanating from, for example, a circuit board. The spectrumanalyzer is capable of identifying the peak intensities of the RF as afunction of frequency in the area of the near field probe. In a typicalcircuit board, the number of RF sources should generally be less than10, but depending on the source, can be more. However, this numberdepends on a variety of factors such as the complexity of the board, thequality of manufacturing, and the size of the components on the board.Once the locations of the RF sources are determined, each of the RFleakage characteristics is accurately measured. In addition, a voltmetermay be used to determine the amplitude of each RF source by physicallymoving the voltmeter probe about the RF signal source until the highestvoltage peaks are reached. Additionally, the amplitude of the signal andthe frequency of the RF signal source (with time as the abscissa) isdetermined using the spectrum analyzer. A circuit diagram will help theoperator to identify the sources of the RFI leakage so that the correctcollectors may be used in the collection step 503.

As an example of the detection step 501, FIG. 6 shows multiple leaked RFleaked signals having the following characteristics:

603 RF Leakage #1—60 Hz in frequency and 1.6 Volts in magnitude, from asolder joint 2 mm away from the CPU-between the CPU and a resistor onthe circuit board;

605 RF Leakage #2—300 Hz in frequency and 2.3 Volts in magnitude, frompin #3 of the DRAM; and

607 RF Leakage #3—1200 Hz in frequency and 2.3 Volts in magnitude,radiating above a capacitor.

Frequencies may be much higher or lower and the voltages may behigher/lower than shown in the example above. The locations of thevoltage peaks may be plotted on graph paper (perhaps circular quadpaper) as a function of position. This plot may be used as an aid toaccurately determine RF leakage position.

In one embodiment, leaked RF signals radiated and/or conducted from theelectronics device is collected as shown in block 503. Conductive RFIleakage is collected with conductive RFI collectors and radiative RFIleakage is collected with radiative RFI collectors.

In one aspect of the present invention, the conducted RF energy iscollected using thin coaxial cables connected to each RF conductionpoint on the circuit board. Each coaxial cable will be tuned and/orfiltered to pick up the specific RF frequency or frequencies or range offrequencies or bandwidth at each location. The tuning circuit, in oneaspect of the present invention, may be a tank circuit. A tank circuitis a simple parallel combination of a capacitor and inductor chosen ortuned such that the resonant frequency of the combination matches thefrequency of the RF. In some aspects of the present invention, the thincoaxial cable may be of the copper shielded type. However, in otheraspects, the coaxial cable is chosen based on its ability to carry theparticular RF signal with minimal losses and minimal leakage radiation.In some aspects, the coaxial cable is soldered to the conduction pointon the circuit board.

In other aspects of the present invention, the radiative RF energy iscollected using antennas. In some embodiments of the present invention,small/micro/nano antennas configured to receive RF from specificlocations on a circuit board. This type of collector collects RFelectromagnetic radiation. In one aspect of the invention, the antennasmay be micro-electro-mechanical (“MEMS”) devices. These antennas may besmall enough to fit on a microchip. The antennas may be an array of MEMSantennas or could be just a single antenna. In other aspects of theinvention the antennas may be horn or parabolic antennas configured toreceive the RF electromagnetic radiation. The antennas may be designedto receive a single frequency or a range of frequencies emanating froman RF radiation location. However, in each case, the antenna will bedesigned to receive the range of frequencies emanating from one or moreRF sources on the circuit board. These types of antennas may also beconfigured outside of the electronic device. For example, parabolicantennas might be placed externally around an important storage deviceor router to collect any remaining RF. Parabolic antennas might also beused to collect all radiative RF that is in a particular room. In such acase, parabolic antennas might be placed in each ceiling corner of aroom.

The collectors may be connected to the RF combiner by coaxial cables or. . . some other type of shielded wire such that the RF signals cannotleak. In order to minimize the number of RF leakages that are createdthe number of components and solder joints etc. . . . in the electronicdevice should also be minimized.

In one embodiment, the collected RF signals are summed into one combinedsignal as shown in block 505. In one aspect of the present invention,the RF signals from the collectors 403, 405, 407 are combined using RFcombiner 409 discussed above, for example. The output of the RF combinercontains the summed up RF signals from the collectors.

In one embodiment, the combined RF signals are up-converted to anoptical wavelength and inserted into an optical fiber as shown in block507. In one aspect of the invention, the combined RF signal is inputtedto a fiber optic transmitter where the up-conversion takes place as isknown to those of skill in the art. The combined RF signals areup-converted to an optical signal and outputted to a fiber optic cable.In one aspect of the present invention, the up-converter may be a devicesuch as described in U.S. Pat. No. 8,538,270 by Seidel et al., which ishereby incorporated by reference.

In one embodiment, the optical signal is directed away from the fiberoptic transmitter as shown block 509. In one aspect of the presentinvention, the optical signals are directed away from the fiber optictransmitter on a fiber optic cable. The fiber optic cable is selectedbased on the type of optical signal inserted on to the cable by thefiber optic transmitter 411. Ideally the fiber optic transmitter andfiber optic cable are selected to operate together in an optimalfashion. The length of the fiber optic cable depends on the method usedfor terminating or attenuating the up-converted signal as discussedabove.

In one embodiment, the optical signal is terminated as shown in block511. In one aspect of the present invention, the fiber optic cable isconnected to a heat sink for example heat sink 415, where all of theoptical signals are terminated. In another aspect of the presentinvention, the fiber optic cable is connected to an optical terminator(fiber optic light trap) such as those produced by ThorLabs(www.thorlabs.com). Such an optical terminator is converts the opticalpower into heat and the power is attenuated inside the devices. Opticalterminators can also have heat sink caps such as that discussed in U.S.Pat. No. 7,099,552 by Oron et al., which is hereby incorporated byreference.

FIG. 6 depicts a circuit board with three locations that are to beshielded using the present invention. As discussed above, 603, 605, 607are the three locations on the circuit board that have RF leakage. 603,605, and 607 are merely examples of RF leakage. Actual RF leakage willbe unique and may not resemble anything like 603, 605, and 607.

FIG. 7 depicts a digitally implemented embodiment of the presentinvention.

There are two types of interfering signals that may be generated from anelectronic circuit—digital interfering signals and analog interferingsignals. Digital interfering signals may be characterized by a squarewave, a saw tooth wave or other RF that represents digital RF. If a userseeks to remove only digital interfering signals, then such signals needto be digitally added using digital arithmetic. The digital arithmeticmay comprise floating point arithmetic, binary arithmetic, or binarycoded decimal arithmetic. Digitally adding signals is commonly realizedto be a more accurate addition process than adding/combining analogsignals. If the user seeks to remove any analog interfering signals, theanalog interfering signals should first be converted to digital tominimize inaccuracies in summing analog signals.

If the user seeks to remove both digital and analog interfering signals,all the analog interfering signals must first be separated from thedigital interfering signals. This is done by digitizing the analogsignals, and then adding all the resulting digital signals by means ofdigital arithmetic. At the same time, the digital signals are also addedtogether. Digital RF signals are not purely digital and therefore shouldalso be digitized to smooth the signal before adding the digitalsignals. Finally, the digitized analog signals are added to thedigitized digital signals. This final resultant signal is then convertedback to a large analog signal for up-conversion.

The system of FIG. 7 may implemented instead of the system of FIG. 4where there are digital RF signals and/or for a more accurate additionprocess. 701 is the digitally enabled active RF shielding (“ARFS”)solution of the present invention. 703, 705, and 707 depict N collectors(where N is the total number of collectors). The outputs of thecollectors 703, 705, and 707 may optionally be routed to an enclosureconnector that may be mounted to the outside of the enclosure of theelectronic device as discussed in connection with FIG. 4. This connectoris not shown in FIG. 7.

In FIG. 7, each of collectors 703, 705, and 707 depict collectorscollecting either digital or analog signals. Optionally, a filter (notshown in FIG. 7) may be placed between each of the collectors 703, 705,and 707 and their respective analog-to-digital converters 719, 721, and723 respectively. The filter may be used to isolate certain bandwidthsor frequencies of interest. For example, a high pass filter may be usedto collect only frequencies above a certain threshold frequency. Inanother aspect, a low pass filter may be used to collect onlyfrequencies below a certain threshold frequency. Other filters may beused such as notch filters or band-pass filters. In another aspect, anycombination of filter may be used to isolate certain bandwidths orfrequencies of concern. In some aspects of the present invention, thefilter may in fact be the same as the tuner as mentioned previously withrespect to FIG. 4. The analog or digital signals collected by collectors703, 705, and 707 is then input to analog-to-digital converters 719,721, and 723 respectively. For an analog RF signal, the A/D converterconverts the analog signal into a digital signal. For a digital RFsignal, the A/D converter smooths the signal into binary coded decimal.Analog-to-digital converters 719, 721, and 723 are commonanalog-to-digital converters as is known to one of skill in the art.Optionally, a digital filter (not shown in FIG. 7) may be placed betweeneach of the analog-to-digital converters 719, 721, and 723 and thedigital processor 709. The output of analog-to-digital converters 719,721, and 723 are each inputted to digital processor 709.

In one aspect of the present invention, the digital processor 709 is anyone of the commonly available DSP chips, FPGA, ASIC, or microprocessorssuch as those manufactured by Analog Devices (www.analog.com) and TexasInstruments (www.ti.com). The only requirement of the DSP, FPGA, ASIC ormicroprocessor is that it accept multiple digital signals and be capableof summing them together to form a single summed digital output. Theoutput of the digital processor 709 connects to the input of a digitalto analog converter 717.

The digital to analog converter 717 converts the summed digital signalfrom digital processor 709 to an analog version of the signal. Theoutput of the digital to analog converter 717 connects to the input ofthe fiber optic transmitter 711.

The fiber optic transmitter 711 up-converts the summed analog signals toan optical signal as fiber optic transmitter 411 as discussed above inconnection with FIG. 4. The fiber optic transmitter outputs theup-converted signal to a fiber optic cable 713. The fiber optic cable713 is the same as the fiber optic cable 411 in FIG. 4 and will not bediscuss further here. The fiber optic cable 713 terminates into aheatsink 715. The heat sink 715 is the same as heatsink 415 and will notbe discussed further here.

FIG. 8 depicts a flow diagram of a process for providing digital ARFS.The process may be performed by some or all of the system of FIG. 7.Process elements in FIG. 8 may be executed individually or incombination with any of the elements of FIG. 7. The detection 801,collection 803, up-conversion 811, direction 813, and termination 815steps of FIG. 8 are the same as that of the detection 501, collection503, up-conversion 507, direction 509, and termination 511 steps of FIG.5, respectively. The combining step 505 of FIG. 5 is replaced by steps805, 807, and 809 of FIG. 8 for the digital implementation.

In one embodiment of the digital implementation, each of one or moreanalog collected signals is converted to digital signals usinganalog-to-digital converters as shown at block 805. The output of eachof the one or more of the analog-to-digital converters is a digitalsignal that represents the original analog collected signal.

In one embodiment, all of the one or more digital signals are summedinto one combined digital signal as shown at block 807. In one aspect ofthe present invention, the digital signals from the analog-to-digitalconverters are combined using digital processor 709. The output of thedigital processor contains the combined digital signals from thecollectors.

In one embodiment of the digital implementation, the process convertsthe combined digital signal to a combined analog signal, block 809. Inone aspect of the present invention, the process converts the combineddigital signal into a combined analog signal using a digital-to-analogconverter such as 717, for example. The output of the digital-to-analogconverter contains the combined analog signals that originated from thecollectors.

In one embodiment of the digital implementation, the process up-convertsthe combined analog signals to an optical wavelength and inserts theup-converted signal to an optical fiber, block 811. In one aspect of theinvention, the combined analog signals are input to a fiber optictransmitter where the up-converting process takes place as is known tothose of skill in the art. The combined analog signals are up-convertedto an optical signal and outputted to a fiber optic cable. In one aspectof the present invention, the up-converter may be a device as describedin U.S. Pat. No. 8,538,270 and is hereby incorporated by reference.

In one embodiment of the digital implementation, the process directs theoptical signal, block 813. In one aspect of the present invention, theoptical signals are directed on a fiber optic cable away from the fiberoptic transmitter. A fiber optic cable is used to direct the signalsfrom the output of the fiber optic transmitter.

In one embodiment of the digital implementation, the optical signal asshown in block 815. In one aspect of the present invention, the fiberoptic cable is connected to a heat sink for example heat sink 715, whereall of the optical signals are terminated.

The present invention may also be used to reduce, minimize or terminatevoltage and/or current spikes due to shock, vibration, heat or coldapplied to an electronic device. In a similar way collectors are placein strategic locations on a circuit board such as the board in FIG. 6.Voltage and/or current transients and spikes are located and measured.Using the system of FIG. 4 or FIG. 7 these transients are removed fromthe system. Taking out the voltage and/or current transients and spikesprotects the overall circuit.

While the present invention has been described with respect to variouspreferred embodiments, it shall be understood that various other changesand modifications may be made to the invention in accordance with thescope of the claims appended hereto.

We claim:
 1. A system for removing at least some radio frequencyinterference emissions, the system comprising: one or more collectors,each of the one or more collectors tuned to one or more bandwidths ofthe at least some radio frequency interference emissions, at least someof the one or more collectors adapted to collect one or more analogsignals; one or more analog-to-digital converters adapted to converteach of the one or more analog signals to digital signals; one or moredigital processors adapted to sum the digital signals into a summeddigital signal; one or more digital-to-analog converters adapted toconvert the summed digital signal to a summed analog signal; and a fiberoptic transmitter adapted to up-convert the summed analog signal into anoptical signal.
 2. The system of claim 1, further comprising atermination device for terminating the optical signal.
 3. The system ofclaim 2, wherein the termination device comprises one or more of: afiber optic cable; and a heat sink.
 4. The system of claim 3, whereinthe fiber optic cable comprises one or more patches.
 5. The system ofclaim 2, wherein the system removes one or more of: most of any radiofrequency interference emissions from one or more of an electronicdevice and a circuitry; or all radio frequency interference emissionsfrom one or more of an electronic device and a circuitry.
 6. The systemof claim 1, wherein at least one of the one or more collectors isadapted to collect one or more second digital signals, wherein at leastone of the one or more digital processors is adapted to sum the digitalsignals with the second digital signals into the summed digital signal.7. The system of claim 1, further comprising: one or more filtersadapted to isolate the one or more bandwidths.
 8. The system of claim 7,further comprising: one or more pre-filters configured to be one or moreof: a high pass filter; a low pass filter; a band-pass filter; and anotch filter.
 9. The system of claim 7, wherein at least one of the oneor more filters are pre-filters.
 10. A system for removing at least someradio frequency interference emissions from an electronic device, thesystem comprising: one or more collectors, each of the one or morecollectors tuned to one or more bandwidths of the at least some radiofrequency interference emissions, at least some of the one or morecollectors adapted to collect one or more analog signals; one or moreanalog-to-digital converters adapted to convert each of the one or moreanalog signals to digital signals; one or more digital processorsadapted to sum the digital signals into a summed digital signal; one ormore digital-to-analog converters adapted to convert the summed digitalsignal to a summed analog signal; and an enclosure connector for routingthe one or more signals, the enclosure connector adapted to connect toan up-conversion device, wherein the up-conversion device comprises: afiber optic transmitter adapted to up-convert the one or more signalsinto an optical signal; and a termination device adapted to terminatethe optical signal.
 11. The system of claim 10, wherein the terminationdevice comprises one or more of: a fiber optic cable; and a heat sink.12. The system of claim 11, wherein the fiber optic cable comprises oneor more patches.
 13. The system of claim 10, wherein the system removesone or more of: most of any radio frequency interference emissions fromone or more of an electronic device and a circuitry; or all radiofrequency interference emissions from one or more of an electronicdevice and a circuitry.
 14. The system of claim 10, wherein at least oneof the one or more collectors is adapted to collect one or more seconddigital signals, wherein at least one of the one or more digitalprocessors is adapted to sum the digital signals with the second digitalsignals into the summed digital signal.
 15. The system of claim 10,further comprising: one or more filters adapted to isolate the one ormore bandwidths.
 16. The system of claim 15, further comprising: one ormore pre-filters configured to be one or more of: a high pass filter; alow pass filter; a band-pass filter; and a notch filter.
 17. The systemof claim 15, wherein at least one of the one or more filters arepre-filters.
 18. A system for removing at least some radio frequencyinterference emissions from an electronic device, the system comprising:one or more collectors, each of the one or more collectors tuned to oneor more bandwidths of the at least some radio frequency interferenceemissions, at least some of the one or more collectors adapted tocollect one or more analog signals; an enclosure connector for routingthe one or more signals, the enclosure connector adapted to connect toan up-conversion device, wherein the up-conversion device comprises: oneor more analog-to-digital converters adapted to convert each of the oneor more analog signals to digital signals; one or more digitalprocessors adapted to sum the digital signals into a summed digitalsignal; one or more digital-to-analog converters adapted to convert thesummed digital signal to a summed analog signal; a fiber optictransmitter adapted to up-convert the one or more signals into anoptical signal; and a termination device adapted to terminate theoptical signal.
 19. The system of claim 18, wherein the terminationdevice comprises one or more of: a fiber optic cable; and a heat sink.20. The system of claim 19, wherein the fiber optic cable comprises oneor more patches.
 21. The system of claim 18, wherein the system removesone or more of: most of any radio frequency interference emissions fromone or more of an electronic device and a circuitry; or all radiofrequency interference emissions from one or more of an electronicdevice and a circuitry.
 22. The system of claim 18, wherein at least oneof the one or more collectors is adapted to collect one or more seconddigital signals, wherein at least one of the one or more digitalprocessors is adapted to sum the digital signals with the second digitalsignals into the summed digital signal.
 23. The system of claim 18,further comprising: one or more filters adapted to isolate the one ormore bandwidths.
 24. The system of claim 23, further comprising: one ormore pre-filters configured to be one or more of: a high pass filter; alow pass filter; a band-pass filter; and a notch filter.
 25. The systemof claim 23, wherein at least one of the one or more filters arepre-filters.